In a normal trailer assembly, the same fasteners are used to connect the door hinges, latches, and locks, as are used on the side panels of the trailer. The fasteners are adequate for the side panels which are attached to the frame and have no freedom of movement. Conversely, the fasteners used on trailer door hinges, latches, and locks are subject to greater shearing forces caused by the weight of the door and the shifting of the trailer from side-to-side during transit. As a result, the fasteners on the doors fail in shear at a much higher rate than is commercially acceptable. Therefore, the trucking industry requires a fastener designed to withstand repeated application of shear forces.
One type of fastener currently used to secure truck trailer door hinges, latches, and locks is a two-part unthreaded assembly composed of a nut and an unthreaded bolt with rings around the bolt shank. The bolt goes through the trailer door panel and hinge plate, and the nut is placed over the rings on the bolt. The nut is squeezed to conform to the bolt, and the excess portion of the bolt is broken off. This type of nut and unthreaded bolt has an unacceptably high rate of failure when used to fasten trailer door hinges, latches, and locks.
Another type of fastener currently used is a T-nut assembly. The T-nut assembly is composed of a T-nut and a bolt with a knurled portion and a threaded portion of a smaller diameter than the knurled portion. The T-nut and bolt assembly is supplied in standard lengths which do not allow for all variations in door panel and hinge plate thicknesses. As a result, the smaller surface area of the bolt in the T-nut assembly is sometimes subjected to the maximum shear forces present at the interface between the door panel and the hinge plate. Additionally, the threads on the bolt are not always completely engaged by the threads of the T-nut, thereby leaving the smaller diameter threaded portion exposed and reducing the strength of the T-nut assembly against shearing, bending, and axial forces. These factors result in an unacceptably high rate of failure of this type of T-nut and bolt assembly when used to fasten trailer door hinges, latches, and locks.
Accordingly, it is desired to provide a trailer door fastener which can withstand repeated application of shearing and bending forces with failure occurring only after an acceptable number of cycles. Further, it is desired to provide a fastener which has a unique length based on the thickness of the door panel and hinge plate which it fastens.